The present invention relates to a method for operating an open end spinning device comprising a spinning rotor and an opening roller, which can be driven individually, and controlled independently of one another. More particularly, the invention relates to such a method wherein, after an interruption of the spinning process has taken place as a result of the detection of the absence of a thread, a piecing process is introduced, in which an upper thread passes through a fiber ring formed in the spinning rotor and is connected thereto, as well as a subsequent drawing in accumulation, which is used to reduce a thin point in the thread following the piecing.
With increasing requirements of the yarn production process, higher and higher demands are also being made on the production of piecings. The process for forming piecings after thread interruptions, the piecing, is generally carried out at the individual spinning stations of the open end rotor spinning machines by a piecing mechanism travelling along the spinning machine, the so-called piecing carriage.
After a thread break, for example, which triggers the piecing, it takes different lengths of time as a function of the position of the piecing carriage at the open end rotor spinning machine until spinning can start again at the relevant spinning station. During the thread break, the drawing in of the fiber is switched off, but the opening roller, which continues to run, still releases fibers at this time from the tuft. In order to achieve the same conditions during piecing and therefore as far as possible the same prefeed quantity of fibers, the tuft is leveled before each piecing.
The actual process of piecing begins with the start of the spinning rotor. In the time after the tuft levelling of the fiber band presented until the drawing in for the operational fiber feed is switched on, fibers are in turn combed out from the tuft of the fiber band and sucked off via the rotor edge of the stationary spinning rotor.
In addition to the after-running of the fiber flow after switching off the drawing in and the delayed start-up after switching on the drawing in, the fiber flow may also react with a delay on increasing the drawing in speed. This can lead to the thread becoming too thin during the run-up of the spinning rotor. This occurs to a particularly marked extent at low drawing in speeds. To avoid this undesired thickness deviation, a drawing in accumulation process can be carried out. Drawing in accumulation processes of this type during piecing are described in detail, for example, in DE 40 30 100 A1 or in the publication by Raasch et al “Automatisches Anspinnen beim OE-Rotorspinnen”, Melliand Textilberichte April 1989, pages 251 to 256.
A single motor-driven opening roller for an open end spinning device is known from German Patent Publication DE 103 38 842 A1. The opening roller known from this document is used on the open end spinning device in the manner already described in the prior art mentioned above.
It has proven to be disadvantageous that the delay described at the outset also occurs here when providing the required fiber quantity for piecing that is necessary for the drawing in accumulation. However, it is important for the quality of the piecings that the fiber supply takes place in a reproducible manner and without a delay.